1. Field of the Invention
The present invention relates to a thin film deposition system for depositing thin films while simultaneously utilizing the strong reaction of the chemical vapor deposition (CVD) process and the film growth in a high vacuum of the physical vapor deposition (PVD) process, and also for easily depositing compound thin films.
2. Prior Art
Among well known thin film deposition systems for depositing thin films on substrates are CVD and PVD systems. The CVD systems provide a strong reactive process, whereas the PVD systems can deposit dense, strong thin films in a high vacuum.
There have been proposed various thin film deposition systems and processes based on the CVD and PVD principles. However, these conventional thin film deposition systems have been disadvantageous in that a substrate and a thin film deposited thereon are not intimately joined together, it is difficult to deposit a thin film on a substrate which is not resistant to heat, and desired compound thin films cannot easily be deposited.
Various efforts have been made to solve the above problems. One attempt is directed to a thin film deposition system known as an ion plating system. In the ion plating system, a hith-frequency electromagnetic field is generated between an evaporation source supporting an evaporant and an object on which a thin film is to be deposited, thereby ionizing the evaporant which is evaporated in an active gas or an inert gas and depositing the ionized evaporant as a thin film on the object in a vacuum. According to another proposal, a DC voltage is applied between an evaporation source and an object on which a thin film is to be deposited in a thin film deposition system known as a DC ion plating system. For further details, reference should be made to Japanese Patent Publications Nos. 52(1977)-29971 and 52(1977)-29091, for example.
Still another thin film deposition system which has been proposed to eliminate the drawbacks is disclosed in Japanese Laid-Open Patent Publication No. 59(1984)-89763. In the disclosed system, a substrate is held on an electrode confronting an evaporation source, a grid is disposed between the confronting electrode and the evaporation source, and a filament for emitting thermions is disposed between the grid and the evaporation source. The grid is held at a positive potential with respect to the filament while a thin film is being deposited on the substrate.
More specifically, the material which has been evaporated from the evaporation source is ionized by thermions emitted from the filament and the ionized material is accelerated by an electric field directed from the grid toward the confronting electrode when the ionized material passes through the grid. The accelerated ionized material impinges upon the substrate, whereupon a thin film is deposited on the substrate in intimate adhesion thereto.
With the conventional thin film deposition systems, it is possible to deposit a thin film which is of a compound of an evaporated material and a gas introduced in an evacuated casing. However, since the gas molecules in the evacuated casing are spread into the entire space in the evacuated casing, they may not effectively contribute to the reaction with high probability.
Furthermore, when an insulative thin film is deposited on a substrate by the known thin film deposition systems, the insulative thin film covers the confronting electrode and the inner surface of the evacuated casing. As a result, an arc discharge may be produced by an electric field directed from the grid toward the confronting electrode and the inner surface of the evacuated casing, whereupon the plasma may be rendered unstable and no good thin film may be deposited.